A solid state imaging device is a semiconductor device which includes a plurality of pixels having a photoelectric conversion element and a metal oxide semiconductor (MOS) transistor which selectively reads a signal stored in the photoelectric conversion element on a substrate and further includes a multi-layered wiring layer on an upper portion thereof. The solid state imaging devices have been used for, for example, a video camera, a digital still camera, or the like. Among the solid state imaging devices, a CMOS-type solid state imaging device manufactured in a complementary MOS (CMOS) process has merits in terms of low voltage and low power consumption. The CMOS-type solid state imaging device has attracted attention as an imaging device for a camera for a mobile phone, a digital still camera, a digital video camera, and the like.
In the solid state imaging device of the related art, light is incident from a multi-layered wiring layer side, and thus, the light is blocked by the multi-layered wiring layer or the like, so that sufficient light collection characteristic cannot be obtained. Therefore, recently, a rear surface incidence type solid state imaging device where light is incident from a rear surface side of a substrate and is photoelectrically converted in an inner portion of the substrate has been manufactured.
As an image quality of a camera is demanded to be improved, implementation of high pixel density and high sensitivity of the solid state imaging device have been tried by scaling a pixel portion which is a light receiving portion while maintaining a chip area so as to increase the number of pixels. In the current state, in a rear surface illumination type solid state imaging device, although the downsizing proceeds to a degree that the unit pixel pitch becomes 1.4 μm, in order to maintain an absorption sensitivity for red light from an optical absorption coefficient of silicon, a thickness of the solid state imaging device is not less than about 3 μm, so that the downsizing proceeds only in the plane direction but the downsizing does not almost proceed in the thickness direction. Since the downsizing does not proceed in the thickness direction, there are several problems of color mixing due to intrusion of red light into neighboring pixels, requirements of high acceleration implantation for formation of an element isolation portion having a depth of 3 μm, and the like.
Therefore, as a method of implementing the downsizing in the thickness direction in the rear surface illumination type solid state imaging device, a technique has been proposed where light incident on the photoelectric conversion element is reflected and the light is returned to the photoelectric conversion element to be used again, so that the thickness of the photoelectric conversion element is reduced by half. As a method of reflecting the light, for example, a metal film may be disposed on a bottom of an interlayer film of a multi-layered wiring layer. However, since a pixel portion of the solid state imaging device is very vulnerable to metal contamination, in a case where a metal layer is disposed directly on the pixels without an interlayer film interposed, fixed pattern noise due to metal contamination may be increased.
In addition, as another method of reflecting the light, a photonic filter referred to as a guided-mode resonance grating, which reflects only a resonance wavelength by using a difference in refractive index between materials and a fine grating structure, may be disposed on the photoelectric conversion element which is a light receiving portion. However, in this case, fixed pattern noise may be increased by damage due to reactive ion etching (RIE) during the formation of the guided-mode resonance grating on a surface of the light receiving portion.